1. Field of the Invention
The present invention is generally related to a method for detecting small quantities of chlorine and ozone in water. More particularly, to using the hydrochloride salt of a para-substituted phenylene ring compound where the substituent moieties are selected from the group consisting of aminoalkyl rings and alkyl rings as a colorimetric reagent for detecting the presence of small quantities of chlorine or ozone in water. Still more particularly, to using the hydrochloride salt of compounds such as 1,1'-para-phenylene dipiperidine and 1,1'-para-phenylene dipyrolidine as colorimetric reagents.
2. Description of the Prior Art
Chlorine and chlorine dioxide are commonly used as disinfectants in the treatment of potable water supplies. Ozone is sometimes employed as a chemical oxidant for removing various constituents from water. For example, manganese, cyanide ion, sulfide ion, and nitrite ion can all be removed with ozone. Ozone is not normally used as a disinfectant because of its short half life in water. In addition, ozone produces oxygen as it decomposes which aerates the water and may actually enhance the potential for regrowth of microorganisms. For this reason, ozone oxidation treatment of a water sample is usually followed by the addition of small quantities of chlorine or chlorine dioxide for disinfecting purposes.
The presence of either residual chlorine or ozone in drinking water poses particular health risks. The Environmental Protection Agency (EPA) will be promulgating standards which limit the residual amount of chlorine and ozone which can be present in drinking water. Several methods have been developed for determining the amount of chlorine in solution. For example, the presence of chlorine is determinable using ultraviolet, continuous amperometric titration, iodometric, colorimetric, and electrode methods. Some methods are specific for free chlorine (Cl.sub.2, HOCl, and OCl anion) while others measure total chlorine (free chlorine plus chloramines and organically bound chlorine).
In the ultraviolet (UV) methods, chlorine is detected by absorption in the UV range. This method is only suitable for qualitative measurements because the molar absorptivities of the chlorine and chloramine species are quite low. The continuous amperometric titration method is considered a standard for routine laboratory measurements. However, a more experienced analyst and extremely clean working conditions are required for conducting a continuous amperometric titration. It has also been found there are statistically significant differences between the results obtained using membrane electrodes (electrode method) and the results obtained by amperometric titration. It is possible that the membrane electrodes provide a free chlorine reading, while the amperometric electrodes measure the sum of free and organically combined chlorine. In the iodometric titration, high concentrations of total chlorine are measurable.
Because of their ease of use, colorimetric methods are preferred for measuring chlorine. N-N-diethyl-p-phenylene diamine sulfate, or DPD salt, which is available from LaMotte Chemical Products Co. or the HACH Co., is the most widely used colorimetric reagent for measuring chlorine on the market. Very low levels as well as high levels of chlorine are quantifiably determinable using DPD. Syringaldazine, commonly known as "FACTS", is another colorimetric reagent for determining the chlorine concentration in solution. The results achievable with FACTS are comparable to the widely accepted DPD test. However, the major disadvantage with FACTS is the difficulty in dissolving syringaldazine. Both FACTS and DPD operate on non-reversible reaction principles, i.e., each requires an oxidative step which produces a colored product that is measured. Both FACTS and DPD tests must be conducted under controlled pH conditions.
Leuco crystal violet (LCV), which has the chemical formula 4,4,4-methyldynetris-(N,N-dimethylaniline), is yet another chemical used for the determination of chlorine in drinking water. This method is capable of determining all of the chloramines as well as free chlorine. The precision of LCV is equivalent to other colorimetric methods, such as DPD and FACTS.
Both the DPD and amperometric titration methods for measuring free available chlorine are subject to interference from monochloramine and dichloramine. The measured free available chlorine concentration in the presence of chloramines is often significantly larger than the true free available chlorine residual. Interference of chloramines can be reduced when using the DPD method by executing rapid titrations. In addition, it has been found that it is beneficial to add small quantities of thioacetamide to the solution when using DPD to test for free chlorine. Mercuric chloride is also known to minimize the affect of chloramines on the free chlorine measurement when testing by DPD. Chloramine interference in the amperometric titration can be reduced by maintaining a 200 millivolt positive potential on the platinum electrode.
Presently, the recommended method for detecting residual ozone in solution is by the use of the Indigo trisulfonate reagent. This method is based on a measure of the decolorization of the indigo blue color by ozone. The Indigo method is rapid and stoichiometric.
Both DPD and FACTS can also be used to detect ozone. However, the accuracy obtainable when testing for ozone with these reagents may be impaired by the presence of other highly oxidative reactants in solution, i.e., all oxidants capable of oxidizing iodide ion such as halogens, manganese oxides and ozone decomposition byproducts. Generally, other colorimetric methods are more reliable for ozone detection.
Therefore, a need exists for reagents which can detect low levels of chlorine or ozone, and which are less subject to chloramine or other oxidizing agent interferences. In addition, a need exists for reagents which are easier to handle and do not require buffering the solution under test.